The vertebrate skeleton forms by endochondral and intramembranous bone formation. During endochondral bone formation, mesenchyme condensations give rise to cartilages that are eventually replaced by bone. However, there are some permanent cartilages that do not ossify, such as the cartilage of the trachea and articular cartilage of the joints, and intramembranous bone formation occurs directly without a cartilage template. This article describes a method for simultaneously visualizing cartilage and mineralized tissues (notably bone) in the developing mouse. It makes use of alcian blue and alizarin red stains, and it is best used for later fetal, newborn, and early post-natal stages of development. Neonatal skeletons are especially well suited for this technique.